Match Play
Once you have logged into the arena, it is quite simple.
1) Go to the hangar and select your plane.
2) After you have selected your plane, then return to the tower.
3) Now you will see the option menu for "Match Play". If you see a number, other than zero, next to an option, it means those players are waiting for the slot to fill.
Once the slots are all filled, the game will launch you. Be careful as there is an invisible wall around your group. It is shown on the clipboard, and there is an audible warning when you start getting close to it. Crossing that line will result in your death.
Now, go get some!